This unit isn't as quiet as a good window air conditioner or through-the-wall air conditioner but for a portable air conditioner it's as quiet as one can be at 52 dB.  I shopped extensively online and while I did find one or two others with lower sound ratings, they weren't dual hose models like this one which cool better than single hose models.  If you want to go with a portable you have to accept the fact that in the current state of the art they just make more noise than the other types.  The trick is finding one whose higher-than-the-other-types noise level is acceptable.  This is a unit whose noise level you can live with rather than always being bothered by it and not being able to do anything about it.

I'm using it in a bedroom with a south facing window on the top floor  of my building (hot attic above) to augment the through-the-wall air conditioner in the living room of my one bedroom unit.  It's eliminated the problem of cool air not reaching the bedroom.

Very satisfied.